Foam materials are a class of commercially and industrially important chemical-based materials. Foams can be prepared by aerating a foaming composition (i.e., entrapping air in a foaming composition), which can be derived by diluting a concentrated precursor. Many foams require certain physical properties to be appropriately useful in desired applications. Among preferred physical properties for foams is the property of stability, to allow the foam to be in a useful form over an extended period of time and therefore useful where an especially stable foam can be desirable, e.g., fire prevention, fire extinguishment, vapor suppression and freeze protection for crops. Further uses include the reduction of surface tension for desirable penetration of fuels and wetting of surfaces, eg. fire extinguishment, surface cleaning/decontamination and surface preparation (such as for concrete surfaces).
An important class of commercial foams includes aqueous film-forming foams (e.g., AFFFs and FFFPs), which aqueous compositions typically contain fluorochemical surfactants, non-fluorinated (e.g., hydrocarbon) surfactants, and aqueous or non-aqueous solvents. These foams can be prepared from concentrates by diluting with water (fresh, brackish or sea water) to form a “premix,” and then aerating the premix to form a foam.
The foam forming composition is conveniently manufactured as a concentrate, to save space and reduce transportation and storage costs. The dilution prior to use of the concentrate is typically 3% concentration by volume (that is, 3 volumes of foam concentrate per 97 volumes of water). Other typical concentrations include 6% concentration by volume and 1% or less concentration by volume.
The foam can be dispersed onto a liquid chemical fire to form a thick foam blanket that knocks down the fire and then extinguishes the fire by suffocation. These foams also find utility as vapor suppressing foams that can be applied to non-burning but volatile liquids, e.g., volatile liquid or solid chemicals and chemical spills, to prevent evolution of toxic, noxious, flammable, or otherwise dangerous vapors. These foams can also be used on structural and bush or forest fires.
Individual components of a foaming composition contribute toward different physical and chemical properties of the premix and the foam. Selective surfactants can provide low surface tension, high foamability, and good film-forming properties, i.e., the ability of drainage from the foam to spread out and form a film over the surface of another liquid. Organic solvents can be included to promote solubility of surfactants, to promote shelf life of the concentrate, and to stabilize the aqueous foam. Thickening agents can be used to increase viscosity and stability of the foam. Other agents and additives can be used as is known to those skilled in the art.
Especially preferred properties of foams are stability, vapor suppression, and burnback resistance. Stability refers to the ability of a foam to maintain over time its physical state as a useful foam. Some fire-fighting foams, e.g., foams prepared from foaming premix compositions containing surfactant and hydrated thickener, are stable for periods of hours, or at least up to an hour, and are often regularly reapplied. Longer periods of stability can be achieved by adding ingredients such as reactive prepolymers and crosslinkers, polyvalent ionic complexing agents and proteins.
The use of fluorochemical compounds in foaming compositions for fire fighting is wide spread for example as taught in U.S. Pat. Nos. 3,772,195; 4,472,286; 4,717,744; 4,983,769; 5,086,786 and 5,824,238. The fluorinated compounds are generally used as surfactants to reduce the surface tension of the foaming composition. However, the production and use of certain fluorochemicals is being reduced and/or phased-out due to concerns associated with such chemicals and/or their use.
Natural compounds such as protein and polysaccharide additives to fire fighting foam solutions are also known. In particular, polysaccharides have been utilised in many forms including cellulose and its derivatives, guar gum, xanthan gum, and polysaccharide derivatives including molasses and other extractions including formoses, in addition to disaccharides and monosaccharides. The use of these materials in fire fighting foams are disclosed for example in patents U.S. Pat. No. 2,514,310 (1946), JP 53023196 (1978), DE 2937333-A (1981), GB 2179043-A (1986), U.S. Pat. No. 4,978,460 (1988) and U.S. Pat. No. 5,215,786 (1993).
U.S. Pat. No. 2,514,310 describes a composition suitable for production of fire extinguishing foams containing an aqueous solution of an N-acyl, N-alkyl taurine sodium salt and a carboxymethylcellulose sodium salt. The compositions of the invention produce fire extinguishing foams highly effective for extinguishing liquid fires.
JP 53023196 describes the use of carboxymethylated yeast-based protein fire extinguishing solutions. The solutions are especially useful for treating large scale fires; the foams having good heat and oil resisting properties.
DE 2937333-A describes a water composition for extinguishing fires which contains a fire-retardant additive and optionally a wetting or foaming agent, preservative, phosphates, nitrogen compounds and further additives. The fire-retardant additive for use in the invention is a polysaccharide or compounds of this type which include molasses and/or formoses (being formaldehyde polymers).
GB 2179043-A describes aqueous foams primarily for use in the food industry as meringues and cake mixes. The foams are formed when compositions containing one acidic foamable protein, preferably whey protein isolate or bovine serum albumin, and a cationic polysaccharide, preferably chitisan. The aqueous foam composition can additionally contain a soluble sugar such as sucrose.
U.S. Pat. No. 4,978,460 is directed to additives for water for the use in fire fighting compositions containing strongly swelling water-insoluble high molecular weight polymers as a gelatinising agent. The improvement to which the specification is directed relates to the use of release agents to encase and disburse the gelatinising agents protecting them from becoming sticky upon the penetration of water and dust from agglutinating. The preferred release agents of the invention are polyalkylene glycols. Further compounds including diammonium phosphates and sugars such as sugar alcohols including mannitol are described as being suitable for use as the release agent.
U.S. Pat. No. 5,215,786 describes compositions for forming a biodegradable foam barrier between a substrate and the atmosphere. The foam-forming composition includes sodium sulphonate, a long alkyl chain carboxylic acid, potassium hydroxide, potassium silicate, a non-ionic solid organic water soluble material such as a sucrose or urea, and a hydroxylic solvent.
Despite the number of foaming compositions known, the continual threat of fire to property, structures, goods and the bush and the destruction, devastation and loss of life it causes means that there is an ongoing need for new, improved or at least alternative aqueous foaming compositions, foam compositions, and methods of preparing foaming compositions. There also is a particular need for preparing foam compositions that are substantially or totally biodegradable and/or environmentally compatible.